Recursive Definitions - CS101 - UdacityYouTube↗  IA↗(long shot)
Education  1.3K views 9 likes 1 dislikes   02 Jun 2012
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[Evans] This works for things other than words.
除了 word 之外，它還可以用於其他事物
The place where you've seen it the most so far has been in language,
目前為止，你看到的它被使用得最多的地方，是語言
but we're also going to see how to use it to make procedures,
但是我們要來看看如何用它來寫程序
and you'll also see how to use it in later classes
在稍後的課程中，你會看到如何來使用它
how to define data structures.
如何定義資料結構
There are lots and lots of different things in computing that are defined recursively.
在計算中，有很多不同的事物是以遞迴來定義的
A recursive definition has 2 parts.
一個遞迴定義有 2 個部分
It has the base case.
它有個基本情況
In our example with the word, that was the second rule.
在 word 的例子中，這是第二個規則
And the base case we can think of as a starting point.
我們可以將基本情況視為一個起點
The important thing about the base case is it's not defined in terms of itself.
關於基本情況很重要的一點是，它並未根據本身的定義
It has to be something where we already know how to define it.
它必須是我們已知要如何定義的事物
So for programs it's usually going to be the smallest input
所以對於程式來說，它往往是最小的輸入
or one of the simplest inputs--something where we already know the answer,
或是最簡單的輸入之一，我們已經知道它的答案了
we don't have to do any computation to figure it out.
我們並不需要做任何計算來了解它
The second part is the recursive case,
第 2 部分是遞迴情況
and that is defined in terms of itself.
它是根據本身而定義的
But it shouldn't be defined in terms of itself exactly,
但它不應該完全根據本身來定義
it should be defined in terms of some sort of smaller version of itself.
它應該根據其本身的某種縮小版來定義
We need to make progress to eventually get to the base case.
我們需要取得一些進展，最後到達基本情況
We'll see what that means in programs soon.
我們很快地會看到這在程式中的意義
First we're going to try one other example not in terms of a program
首先我們嘗試另一個例子，它不是程式
just to get a better sense for how things can be defined recursively.
只是為了讓你更清楚地了解，如何對事物進行遞迴定義
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